What does alkaline really means?

Pratyush took sulphur powder on a spatula and heated it. He collected the evolved by inverting a test tube over it. What will be the action of gas on the following?

Dry litmus paper.

Show by the help of an appropriate litmus paper that the aqueous solution of ammonia is alkaline in nature. 

Which acid is present in each of the following? 

(a) Sour milk (b) Tamarind (c) Orange.

Vankarbhaibhas explained the definition of an acid and a base, given by Robert Boyle in the classroom. Then the students of the classroom gave some suggestions regarding acid and base. Which suggestion is wrong among these?

Prashant: Acids are sour in taste and bases are bitter.

Dhruvi: Acid does not give any effect on wet blue litmus paper while base turns blue litmus paper blue.

Seil: Acid liberates dry hydrogen gas $\left({\mathrm{H}}_2\right)$ by the reaction with the metal. The base does not react with all metals.

Jaydeep: By neutralisation reaction between acid and base, salt and water is produced.

Pratyush took sulphur powder on a spatula and heated it. He collected the evolved by inverting a test tube over it. What will be the action of gas on the following?

Moist litmus paper.

An indicator is added to Potassium Hydroxide and the solution turns pink:

What is the colour change you will observe if you add litmus to the same solution?

The salt solution which does not react with ammonium hydroxide is:

What is an alkali? Do basic solutions also have ${\mathrm{H}}^{+}$(aq) ions? If yes, then why are these basic?